Suppression of Supermode and Phase Noises in Mode-Locked Erbium- Doped Fiber Laser with a Semiconductor Optical Amplifier Based High-Pass Filter

摘要

The variations and trade-off between single-sided-band (SSB) phase noise and supermode noise (SMN) suppression ratio of an actively mode-locked erbium-doped fiber laser (EDFL) with intra-cavity semiconductor optical amplifier (SOA) based high-pass filter are discussed. The insertion of an SOA increases the SMN suppression ratio of the EDFL from 26 dB to 41.4 dB, however, the SSB phase noise at 100 kHz offset frequency from carrier is concurrently degraded from -114 dBc/Hz to -96 dBc/Hz. Such an operation also causes a broadening in the EDFL pulsewidth from 36 ps to 130 ps. The insertion of an optical bandpass filter (OBPF) further reduces the SSB phase noise to -110 dBc/Hz and improves the SMN suppression ratio to 43 dB. Theoretical simulation interprets that the optimized operation of the SOA based highpass filter at nearly transparent current condition is mandatory to achieve a better SMN suppression ratio and minimize the SSB phase noise of the mode-locked EDFL without sacrificing its output pulsewidth.